This invention relates to a color television picture tube base-socket system for connecting a color television picture tube to a television chassis. Typically, a cathode ray tube used as a picture tube in a television receiver has a plurality of pins extending from a base for plugging into a socket which is connected to the chassis. The base is attached to the end of a neck of the color television picture tube. The pins are generally arranged in a ring and a voltage in the range of a few hundred volts or less is applied to most of the pins. A single pin may be present which has up to about 7500 volts.
In order to prevent damage to the cathode ray tube caused by excessive voltage on the pins, color cathode ray tube sockets are normally provided with some type of safety device in the form of a grounding apparatus. Usually the grounding apparatus permits a spark to jump from a pin contact to ground in the event that the pin contact is receiving an excessive potential. This prevents damage to the tube due to excess potential at one of the pin contacts by providing a nondestructive shunt path for the arc.
It is possible, however, that arcs may occur from a high voltage pin on the base to one or more low voltage pins on the base even when the socket is provided with a grounding apparatus. Conventionally, insulative barriers or walls are molded as part of the base structure so that the pins are separated electrically and physically from one another. The limit to which potentials may increase on the pins before an arc occurs between the pins is dependent on the size and shape of the walls. The farther in distance an arc must travel between pins (the arc path length), the better the arc prevention provided by the base.
This invention has many applications, but is believed to be most advantageously associated with a tube having a unique electron gun as disclosed in U.S. Pat. No. 3,995,194, assigned to the same assignee as the present application. This gun has a main focus lens with three or more electrodes, which receive, in a preferred embodiment, operating potentials of about 30 kV, about 12 kV and about 7.5 kV. The 30 kV electrode receives its operating potential through an electrode which is introduced by means of an anode button, as is conventional. However, the relatively high 12 kV potential, the video signal, and other low potentials, and the relatively intermediate 7.5 kV focus voltage are preferably brought through the base of the tube.
It is desirable that a base-socket system be resistive to arcing when voltage potentials in excess of 12 kV are applied to the pins. These extremely high voltage potentials appear, for example, when a tube arcs during operation due to the presence of impurities inside the tube or when the tube is processed (e.g. spot knocking); potentials as high as 30 kV may occur on the pins. This invention provides a novel base-sockt system which is capable of preventing arcs when excessively high voltages appear on the pins of the tube.
It is well known in the art to extend the arc path by providing axially extending walls around a high voltage pin. If an arc does occur the arc must travel from the high voltage pin over the wall and to the next adjacent pin. U.S. Pat. No. 3,278,886 issued to H. H. Blumenberg et al. discloses a nonconductive shielding wall surrounding a high voltage pin for arc prevention. It is believed that it would be difficult, if not impossible, using the shielding wall disclosed in the Blumenberg patent to provide adequate arc prevention when the operating potential on the pin is as high as 10 to 15 kV. It is certain that the shielding wall would not prevent arcs from occurring when much greater potentials in the range of plural tens of kilovolts might appear on the high voltage pin. These high potentials may appear when a tube arcs during operation or when the tube is being processed (for example, during spot knocking). If the shielding wall were extended in length a distance adequate to provide full arc prevention, the resulting structure would be commercially impractical due to the exended length of the picture tube, and also it is doubtful that such a socket could be molded with present molding techniques.